Exhaust gas recirculation valve with variable flow area

ABSTRACT

A flow control valve having a controllable flow area which varies with the valve displacement. The flow control valve includes a poppet-type valve element mounted to reciprocate between a closed and open position in a valve cavity formed in a valve housing. The valve housing has an inlet and outlet passage to allow fluid to flow therethrough. A removable insert having a flow passage is positioned in the valve cavity adjacent the poppet-valve for controlling the flow rate of gaseous fluid from the inlet passage to the outlet passage while the poppet valve is in an open position. Movement of the poppet valve from a closed to an open position varies the effective cross-sectional flow area of the flow passage.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a control valve for use in an internalcombustion engine and more particularly, to an exhaust gas recirculation(EGR) valve having a controllable flow area that varies with valvedisplacement.

BACKGROUND OF THE INVENTION

Improvements in valve designs used in internal combustion engines tocontrol various functions of the engine and to enhance engineperformance have been ongoing for many years. The quest for an internalcombustion engine having an optimum efficiency has also been on theminds of engine manufacturers over time. By making improvements on valvefunctionality and design, engine manufacturers are able to solve manyproblems experienced by their customers and remain competitive in themarketplace.

One aspect of engine performance that has received attention in recentyears is exhaust gas recirculation, especially in a diesel engine. In adiesel engine, an excess amount of air is usually introduced into thecombustion chamber. Therefore, exhaust gas recirculation operation for adiesel engine must be controlled relative to the excess. Since theamount of excess air decreases in accordance with the increase of engineload, it would be desirable to manufacture a valve device forcontrolling the amount of gas and air directed to the engine in such away that the amount of recirculated exhaust gas introduced into theengine intake passageway is decreased while the amount of intake airdirected to the engine is increased in accordance with an increasingengine load. In order to effectively control exhaust gas recirculation,the relationship between the load of the engine and the ratio of theamount of recirculated exhaust gas to the total mount of fluid directedto the engine should be determined.

Various types of valve designs exist which utilize geometrically shapedopenings to control fluid flow for achieving desired engine operationcharacteristics. One reference which discloses such a design is U.S.Pat. No. 4,154,263 to Cary. This reference discloses a control valvehaving a movable valve element positioned in a cylindrical housing withtriangularly shaped openings formed therein for variably controllingfluid flow depending on the relative position of the valve element. Theapertures may take a variety of shapes to achieve the desired flowcharacteristics with respect to the stem travel. The valve design ofCary, however, includes apertures formed on the upstream side of thevalve which decrease the effective controllability of fluid flow. Inaddition, the valve element of Cary comprises a spool valve structurewhich often does not provide an adequate seal along the slidableclearance between the valve element and housing. The spool valvestructure of Cary also has many parts and is costly to manufacture whichwould make it undesirable for many applications.

Two references which disclose an improvement to the Cary design in termsof enhancing flow characteristics are U.S. Pat. Nos. 5,205,537 and5,368,276, both to Pfeiffer. These references disclose a control valvestructure including a control valve element and a flow orifice or porthaving a variable cross-section (i.e., a teardrop or egg-shaped crosssection). Movement of the valve element varies the cross sectional flowarea based on the shape of the flow port to provide enhanced area andflow range ability. The valve structures of Pfeiffer, however, are spoolvalve designs which are costly to manufacture and may not provideadequate sealing in high pressure environments. In addition, the flowport is formed in the valve element instead of the valve body which alsoincreases manufacture and repair costs. Furthermore, the Pfeiffer valveis designed to control the flow of particulate solids and not gaseousfluids generated by an internal combustion engine.

U.S. Pat. No. 4,237,837 to Toda et al. discloses an exhaust gasrecirculation control valve for a diesel engine that is designed toachieve a low rate of increase in the flow area of the exhaust gas whenthe valve is opened from its fully closed position. Toda et al.discloses a complex valve design comprising many parts for merelyactuating the valve element. In addition, the valve of Toda et al. doesnot provide a downstream outlet port formed in a valve cavity which isdesirable for effective control of flow characteristics.

It is evident, based on the art discussed above, that the manufacturingindustry has yet to develop a simple, inexpensive and compact valve withimproved flow control characteristics for effectively controlling theflow of fluid therethrough.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a flow control valve for effectively controlling EGR flowcharacteristics in an internal combustion engine.

It is further an object of the present invention to achieve the aboveobject, and to provide a flow control valve that is compact andinexpensive to manufacture.

It is also an object of the present invention to achieve one or more ofthe above objects, and to further provide a flow control valve thateffectively controls the degree to which NOx emissions and othercharacteristics are reduced or influenced.

It is a further object of the present invention to achieve one or moreof the above objects and also provide a flow control valve that includesa poppet valve movable within a flow passage for varying and effectivelycontrolling the cross-sectional flow area of the flow passage.

It is a yet another object of the present invention to achieve one ormore of the above objects and also provide a flow control valve thatincludes removable inserts having different flow alteringcharacteristics.

It is also another object of the present invention to achieve one ormore of the above objects and also provide a flow control valve forapplications that demand rapid initial opening and finer flow control athigher valve lifts.

It is yet a further object of the present invention to achieve one ormore of the above objects and also provide a flow control valve forapplications that demand a slower initial opening and finer flow controlat lower valve lifts.

These, as well as other objects of the present invention, are achievedby a flow control valve for controlling the flow of gaseous fluids. Thevalve includes a valve housing having a cavity, an inlet passage, anoutlet passage, and a poppet valve positioned in the cavity whichincludes a reciprocally mounted valve element and a valve seat. Thepoppet valve is movable between an open position in which the valveelement is positioned a spaced distance from the valve seat to permitfluid flow through the cavity and a closed position in which the valveelement engages the valve seat to block flow through the cavity. Thevalve further includes a flow varying means positioned in the cavityadjacent the valve element for controlling the flow rate of gaseousfluids from the inlet passage to the outlet passage during movement ofthe poppet valve. The flow varying means includes an insert and a flowpassage formed in the insert, wherein movement of the valve element fromthe closed to the open position varies the effective cross-sectionalflow area of the flow passage.

Attached to the valve housing is an integral spring seat cap whichencloses a spring means and provides a positive force on the valveelement to maintain a seal between the valve head and valve seat. Theflow control valve further comprises a sensing means rigidly attached tothe integral spring seat cap. In addition, the flow control valveincludes either an apertured insert or a tapered insert positionedadjacent the cylindrical housing, both inserts having a cylindricalshape. The apertured insert includes circular apertures formed in thewall of the insert which are aligned with the outlet passage forpermitting fluids to flow therethrough. The tapered insert has a firstand second opening with a flow varying surface therebetween. The flowvarying surface has a predetermined shape such that movement of thevalve element along the flow varying surface varies an effectivecross-sectional flow area of the flow passage so as to achieve apredetermined flow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a partial cross-sectional view of an exhaust gasrecirculation (EGR) valve with a radial-hole insert in accordance with apreferred embodiment of the present invention;

FIG. 1b is a side elevational view of the radial-hole insert of thepreferred embodiment at 1b--1b of FIG. 1a;

FIG. 2 is an exploded elevational view of a valve stem positionedrelative to a radial-hole insert in accordance with a preferredembodiment of the present invention as shown in FIGS. 1a and 1b;

FIG. 3 is a partial cross-sectional view of an EGR valve with a taperedinsert in accordance with a second embodiment of the present invention;

FIG. 4a is an exploded elevational view of a valve stem positionedrelative to a tapered insert in accordance with the second embodiment ofthe present invention;

FIG. 4b is an exploded elevational view of a valve stem positionedrelative to a variable tapered insert in accordance with a thirdembodiment of the present invention;

FIG. 5 is a graph of an EGR valve lift percentage versus an EGR valveeffective flow area percentage for the radial-hole insert and thetapered insert of the present invention;

FIG. 6 is a graph of an EGR valve flow area percentage versus a valvelift percentage for a variety of tapered insert designs; and

FIG. 7 is a graph of an EGR valve flow area percentage versus a valvelift percentage for a variety of tapered insert designs where theminimum diameter of the taper is somewhat greater than the diameter ofthe poppet head and the inserts graphically represented in FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to an exhaust gas recirculation (EGR)valve for an internal combustion engine which provides improved EGR flowcontrol. The preferred embodiment includes a reciprocally mountedpoppet-type valve for providing optimum EGR flow control in a variety ofconditions. The present invention allows a user to design theinput/output characteristics of the EGR valve specifically for the needsof a particular system. In this context, the "input" to the poppet-typevalve is its linear travel or lift, while its "output" is the amount ofeffective flow area through the valve at a given position. The valve'seffective flow area directly influences the flow rate of the EGR valveand hence the degree to which both NOx emissions are reduced and othercharacteristics, such as particulate emissions and fuel economy, arepositively influenced.

Referring now to the drawings, the preferred embodiments of the presentinvention will be discussed in detail. The structure of the presentinvention will be described with reference to FIGS. 1-4 and itscharacteristics during operation will be explained using graphical dataillustrated in FIGS. 5-7.

FIG. 1a illustrates an EGR valve 1 in accordance with the preferredembodiment of the present invention. EGR valve 1 includes a valvehousing 2, including an upper portion 5 forming an upper cavity 12 and alower portion 7 connected to upper portion 5 in a conventional manner.Lower portion 7 includes a lower cavity 11 and a cylindrical bore 8formed in a neck portion 9 and extending between upper cavity 12 andlower cavity 11. Lower portion 7 also includes an inlet passage 4 and anoutlet passage 6 which allows gaseous fluids to flow into and out oflower cavity 11. In a preferred embodiment, gaseous fluids flow frominlet passage 4 to outlet passage 6, however, in an alternativeembodiment, the inlet and outlet passages may be reversed such thatfluid flows from outlet passage 6 to inlet passage 4 as illustrated inFIG. 1a. One skilled in the art should recognize that even though theflow pattern of the preferred embodiment is discussed herein with regardto the present invention, the flow pattern of the alternative embodimentdescribed above is within the scope of this invention and may bepreferred in particular applications depending on the desired flowcharacteristics of EGR valve 1.

Valve housing 2 also includes a mating flange 13 with a valve gasket 15interposed therebetween. Valve gasket 15 is compressed between valvehousing 2 and mating flange 13 in order to provide an effective seal toprevent leakage of fluid at high engine pressures. Leakage of fluidduring engine operation can undesirably affect engine efficiency andpower. Mating flange 13 is attached to an external structure (not shown)in a conventional manner and has a ring shape in the preferredembodiment of the invention. A center hole 19 of mating flange 13directs fluid flow into inlet passage 4. An annular portion of the topsurface of mating flange 13 positioned adjacent inlet passage 4 forms avalve seat 21.

EGR valve 1 further includes a valve element 10 reciprocally mounted inupper cavity 12. Valve element 10 includes a valve stem 33 which extendsthrough neck portion 9 and into lower cavity 11, and a valve head 40formed on the lower portion of valve stem 33. Valve head 40 isdisc-shaped and may be formed from the same material as valve stem 33.The valve element is movable between an open position in which valvehead 40 is positioned a spaced distance from valve seat 21, as shown inFIG. 1a, to permit fluid to flow through lower cavity 11, and a closedposition in which valve element 10 engages valve seat 21 to block flowthrough lower cavity 11.

Upper portion 5 of valve housing 2 includes an integral spring seat cap14 that is rigidly attached to lower portion 7 to form upper cavity 12.Compressed between integral spring seat cap 14 and valve housing 2 is agasket 16 for creating a seal to prevent leakage of fluid from valvehousing 2. The upper portion of valve element 10 is positioned in uppercavity 12 in a manner which allows only reciprocating linear movement.Valve element 10 is attached to a piston 20 and a retainer nut 22 whichreciprocate with valve element 10 during movement of the valve from aclosed position to an open position. Also included in upper cavity 12 isa spring 18 which is axially positioned within upper cavity 12. Integralspring seat cap 14 includes a recessed portion 23 for receiving spring18 at one end. Piston 20 includes an annular wall 17 to form a cup-shapewhich allows the other end of spring 18 to fit securely within its innercavity 31 in a compressive abutment. When spring 18 compresses, annularwall 17 of piston 20 act as spring stops against integral spring seatcap 14 to allow valve element 10 to travel only a predetermined distancewhen moving towards an open position.

In the preferred embodiment of the present invention, EGR valve 1 isactuated by air pressure which moves a diaphragm 29 attached to gasket16 and piston 20 between a first and second position. In order for valveelement 10 to move from a closed position to an open position to controlfluid flow rate, air pressure is supplied into a port 25 formed in valvehousing 2 which provides a pressure against the bottom of diaphragm 29sufficient to overcome the resistive force of spring 18. As the airpressure increases, diaphragm 29 and piston 20 move in an upwarddirection towards integral spring seat cap 14. To move valve element 10towards a closed position, the air pressure forcing diaphragm 29 upwardis released through port 25. At this point, the resistive force ofspring 18 is sufficient to force piston 20 downward until valve element10 engages valve seat 21. In certain embodiments, such as the valvestructure shown in FIG. 4b, the spring biases the valve element so thatthe back surface of the valve head seats and seals the valve in a closedposition. In this embodiment, the valve is opened by actuating the valveelement downward, away from the valve seat. One skilled in the artshould recognize that any actuation means (i.e., solenoid, hydraulic,etc.) may be used with this invention to control reciprocal movement ofvalve element 10.

Integral spring seat cap 14 includes an opening 24 at its uppermost endfor receiving a linear position sensor 26 which serves as apotentiometer or a similar type of linear position sensor for EGRvalve 1. Sensor 26 threadingly engages integral spring seat cap 14 andabuts retainer nut 22, which also serves as a position sensor contact,via extension 27 reciprocally attached to the base of linear positionsensor 26. Retainer nut 22 is positioned directly above piston 20 and isconnected to the top portion valve element 10 in a conventional manner.

Linear position sensor 26 records the movement of valve element 10,during operation of EGR valve 1, to track its movement and positionrelative to valve seat 21. This data is useful for determining whetherEGR valve 1 is in an open or closed condition and is also essential incalculating valve lift for achieving the desired flow characteristics ofthe valve structure. For example, if linear flow characteristics aredesired, the valve stem may have a 25% lift (compared to a maximum liftof 100%) to achieve a flow area of 25% (compared to a maximum flow areaof 100%). By regulating the lift or position of the valve element 10,EGR valve 1 can accurately control the rate of gaseous fluid that isable to flow from inlet passage 4 and through outlet passage 6. Theposition of valve element 10 is controlled by movement of diaphragm 29which is repeatable over time, thus, allowing the valve to maintain arepeatable control scheme.

EGR valve 1 further includes a flow varying device 35 including aninsert 36 having a flow passage 28 for permitting the flow of gaseousfluids from inlet passage 4 to outlet passage 6. Insert 36 is acylindrically shaped element secured within lower cavity 11 by a slipfit and is positioned adjacent valve element 10. In order to preventinsert 36 from rotating within lower cavity 11, a set screw may be usedto secure insert 36 to valve housing 2. For insert designs which rely onproper aperture alignment with outlet passage 6 to control fluid flowrate, a set screw or a similar fastening means would be necessary.

Insert 36 is removable from valve housing 2 and may have variousgeometrical shapes and flow passages to create a vast spectrum ofcontrolled flow configurations through EGR valve 1. Insert 36 includes afirst opening 37 positioned adjacent inlet passage 4 of the valvehousing 2 and a second opening 39 opposed to first opening 37 thus,defining flow passage 28 therebetween. In a preferred embodiment, insert36 includes two apertures 38 which are formed in the wall of insert 36,as shown in FIG. 1b. In this embodiment, the apertures have a circularshape. In a second preferred embodiment, the insert may have a taperedinner wall, as discussed in further detail below, or different shapedapertures formed in the wall of the insert. In addition, the insert mayhave one or more apertures positioned along a similar radial plane inthe insert or along different planes, depending the flow characteristicsdesired from EGR valve 1.

Valve head 40 moves within the inner radial extent of insert 36 asclearly illustrated in FIG. 1a. The valve head 40 forms a close slidingfit with the inner wall of insert 36 to create a fluid seal as valveelement 10 moves within flow passage 28, thereby, preventing the flow offluid from first opening 37 through second opening 39. The blockage offluid flowing through the second opening of the insert forces the fluidto flow through an effective cross-sectional area of the aperturesformed in insert 36 based on the position of valve element 10. As valveelement 10 lifts toward an open position, valve head 40 graduallyuncovers a greater portion of apertures 38 to gradually increase theeffective cross-sectional flow area through apertures 38 at apredetermined rate.

The shape and position of apertures 38 are crucial for controlling therate at which the effective flow area of apertures 38 increases.Conventional poppet valves have a tendency to open rapidly, with respectto effective flow area, during the initial range of valve head travel,that is, when the valve head begins to move away from the valve seat toallow fluid to flow therebetween. Consequently, the rate at which theeffective flow area increases with lift falls. The present inventionutilizes aperture geometries and position to control the rate at whichthe effective flow area increases with valve lift. FIG. 1b shows insert36 with two apertures which are formed adjacent one another.Nevertheless, insert 36 may be designed with larger or smaller aperturesor apertures formed in different patterns in the insert. In essence, theaperture size and position may be altered to achieve the desired flowrate control.

FIG. 2 shows an exploded view of valve head 40 with respect to insert 36and apertures 38. As shown by this figure, valve head 40 moving acrossapertures 38 in an upward direction varies flow area 42 of each of thetwo apertures 38 substantially equally. The shape of apertures 38control the amount of fluid allowed to flow through the apertures, whilethe valve lift controls the effective flow area. The circular aperturesof insert 36 allow for a fine degree of control during the initial rangeof valve head travel since only the very bottom portions of theapertures defining a small flow area are exposed to allow fluid to flowtherethrough. If apertures 38 were square and the valve lift relative tothe circular apertures is equal, more fluid would be able to passthrough the square aperture than the circular aperture due to a widerflow area at its bottom portion. Therefore, a circular aperture providesgreater control of flow rate at the initial range of valve head lift asquare aperture, for example, or other similarly shaped aperture. Theflow characteristics of the apertures used in the preferred embodimentsof the present invention are graphically represented in FIG. 5 which isdiscussed in further detail below.

FIG. 3 illustrates a second preferred embodiment of the presentinvention which includes a similar valve structure to that shown in FIG.1, however, the flow varying device includes a tapered insert 48positioned in the lower cavity of valve housing 2. Tapered insert 48 isvery similar to apertured insert 36 (illustrated in FIG. 1) in that bothinserts are removable and cylindrical. Tapered insert 48 may be securedinto valve housing 2 by a slip fit without the need for a set screw. Inaddition, like apertured insert 36, tapered insert 48 is positioneddownstream of valve seat 21 for altering the flow of fluid between inletpassage 4 and outlet passage 6. Tapered insert 48 includes a firstopening 51 for receiving fluid from inlet passage 4 and directing thefluid flow into flow passage 28, and a second opening 53 positioneddownstream of first opening 51 for directing the fluid flow to outletpassage 6. Tapered insert 48 differs from insert 36 by including a flowvarying surface 47 extending between the first and second openings. Flowvarying surface 47 encircles valve head 40 when the valve head ispositioned between the first and second openings to define a flow pathor radial gap in flow passage 28 between flow varying surface 47 andvalve head 40. Flow varying surface 47 has a predetermined shape suchthat the movement of the valve head along flow varying surface 47 towardan open position varies the effective cross-sectional flow area of theradial gap of flow passage 28 in order to achieve a predetermined rateof increase in the flow rate of the fluid passing therethrough.

Flow varying surface 47 of tapered insert 48 includes a frusto-conicalor tapered shape. However, the shape of flow varying surface may bealtered in order to increase or decrease the amount of gaseous fluidable to flow through the radial gap. For example, if an increased flowrate is desired even after the valve element is at maximum lift, thenthe larger diameter portion 49 of tapered insert 48 may be increased toallow a greater volume of fluid to flow therethrough.

FIG. 4a shows an exploded view of valve head 40 in relation to flowvarying surface 47 of tapered insert 48, in accordance with the secondpreferred embodiment of the invention. This figure illustrates an axialgap 52 between valve head 40 and valve seat 21 (illustrated in FIGS. 1and 3) and a radial gap 54 between flow varying surface 47 and the outerannular edges of valve head 40 to control gaseous fluid flow. Pleasenote that the distances of FIG. 4a are not drawn to scale and are merelyshown to define the meanings of axial and radial gap in the presentinvention.

Referring to FIG. 4a, as valve element 10 is lifted from valve seat 21(shown in FIGS. 1 and 3), both axial gap 52 and radial gap 54 increase.Axial gap 52 controls the flow of gaseous fluids during the early partof valve stem lift, while radial gap 54 controls the flow area at liftsgreater than the initial range of lift. The amount of control, if any,of the axial and radial gaps during valve operation will vary dependingon the size and shape of flow varying surface 47 and its positionrelative to valve head 40. The distinctions between the various sizesand shapes of the flow varying surface are discussed in further detailwith regard to FIGS. 6 and 7. As valve head 40 moves along flow varyingsurface 47 of tapered insert 48 toward an open position, the effectivecross-sectional area of flow passage 28 is varied to achieve apredetermined increase in the fluid flow rate. The flow rate iscontrolled based on the effective flow area between valve head 40 andflow varying surface 47. Therefore, assuming the size of valve head 40remains constant, a user may simply vary the shape of flow varyingsurface to obtain the desired flow characteristics for EGR valve 1.

A variation of tapered insert 48 used in EGR valve 1 is illustrated inFIG. 4b. Variable tapered insert 61 includes a flow varying surface 62similar to flow varying surface 47 described above but having aninverted orientation with respect thereto. In this embodiment, theactuation means is similar to that of the preferred embodimentsdiscussed above, however, valve element 10 is biased against valve seat63 in a closed position and extends downward towards an open position toeffectively control the flow rate of fluid from first opening 69 throughsecond opening 71 via radial gap 68. This embodiment may be preferredfor certain applications requiring a back-seated valve structure forflow control.

As described above in reference to the first and second preferredembodiments of the present invention, two types of inserts are used invalve housing 2 for varying the flow characteristics of a valve system.With apertured insert 36, the flow is controlled based on the effectivecross-sectional area of aperture 38 that is exposed by valve head 40while the valve is being lifted, as shown in FIG. 2. However, withtapered insert 48, flow is controlled based on the defined flow area oraxial gap between valve head 40 and valve seat 21 and the radial gapbetween valve head 40 and flow varying surface 47 as the valve head islifted.

FIG. 5 illustrates a graph representing EGR valve effective flow areapercentages versus EGR valve lift percentages for both apertured insert36, as well as tapered insert 48. This figure provides a graphicalrepresentation of flow characteristic data specifically for the twoinsert designs of the first and second preferred embodiments. Using themathematical data from FIG. 6, the relationship of the graph to valveoperation is described as follows: if Z is the lift of the valve and Ais the effective flow area of the valve, then the rate of change or"gain" of the valve will vary, dependent on the lift of the valve. Forthe apertured insert, the curve is concave upward and the gain is low atlow lifts and increases through the entire lift range, as illustrated inFIG. 5. This would be very useful for system architecture that needs afine degree of control at low lifts or flow areas, and perhaps needs alarge range of flow area and can tolerate a coarser control near the topend of travel. The gain of the tapered insert is higher as compared tothe apertured insert when the lift of the valve stem is low. As the liftof the valve stem increases, the tapered insert flow area alsoincreases. However, the flow area begins to taper off after the valve islifted up to around 40% of its maximum lift. The graphical data of FIG.5 illustrates that the tapered insert allows a larger flow area as thevalve lifts than the apertured insert. Nevertheless, the rate of changeor gain of the tapered insert decreases as the valve lift is greaterthan 50%. As can be further seen from the graph, however, the aperturedinsert provides for more accurate control of flow during initial valvestem lift or opening of EGR valve 1. Both inserts provide a significantamount of flexibility for a user to create an appropriate flow controlvalve structure for suiting specific EGR needs.

FIG. 6 graphically represents a variety of tapered insert designs andtheir respective effective flow area schedules to generate a range offlow control characteristics. Each curve corresponds to one taperedinsert design. Specifically, FIG. 6 shows the valve flow area percentageversus the valve lift percentage of the tapered insert used in the EGRvalve of the second preferred embodiment. The legend of FIG. 6illustrates power function exponents which may be used to alter thegraphical representation of the flow rate for the tapered insert design.The mathematical representation of each curve is A=min(A_(axial),A_(radial)), where "A" represents the effective flow area of the valve,"A_(axiai) " represents the axial valve lift percentage, and "A_(radia)" represents the valve flow area based on the radial gap between valvehead 40 and the flow varying surface 47 of the insert.

The A_(axial) value is calculated as follows:

A_(axial) =IIDZ, where "D" represents the diameter of the valve head and"Z" represents the lift of the valve stem during EGR valve 1 operation.

The A_(radial) =value is calculated as follows:

A_(radial) =a+bZ^(n),

where "a" is the diameter of the tapered inner walls of the insert atthe minimum diameter which equals 2.7% of A_(max) or the maximum flowarea of the EGR valve; "b" is a coefficient representing how the taperdiameter increases with valve stem lift; "Z" represents the lift of thevalve stem; and "n" is an exponent representing the unique taperdefinition for each insert represented on the graph of FIG. 6. The valueof A_(axial) is represented on the Y-axis of the graph and the value ofA_(radial) is represented on the X-axis of the graph.

The design of the tapered insert lends itself to more flexibility thanthe apertured insert design with regard to the range of flowability.Using the range parameters discussed above and noted in the legend ofFIG. 6, a user can design: (a) concave downward flow characteristicshapes for situations demanding rapid initial openings and finer controlat the top end of the valve lift (n<1.0), (b) fully linearized flowcharacteristic shapes where the user desires linearized flow control(n=1.0), or (c) concave upward flow characteristic shapes where finecontrol at the bottom end is needed at the expense or coarser control atthe top end (n>1.0). The tapered insert designs graphical represented inFIG. 6 have minimum flow varying surface diameters slightly greater thanthe diameter of the valve head, thus allowing minimal fluid flow whenthe valve is initially opened.

FIG. 7 represents valve flow area percentage versus valve liftpercentage of a tapered insert design used with EGR valve 1 where theminimum diameter of the taper is a predetermined amount greater than thediameter of the valve head and therefore, the initial flow area opens upmost rapidly, being controlled only by the axial gap in an extendedinitial opening period. For example, in FIG. 6 the tapered insert designwith a taper definition exponent of n=1.0, i.e. a flat linear taper witha minimum diameter yielding a radial flow of 30% of the maximum flowarea (this is the middle curve of the five curves), the flow area opensup to 50% of its maximum in the initial 25% of lift, leaving the upper50% of flow area to be controlled with the remaining 75% of lift. Forfiner control at higher lifts, a tapered insert having taper definitionexponent of n=0.5 (the top curve) will provide greater control of theflow rate by controlling the flow through the radial gap between thevalve head 40 and flow varying surface 47 when the valve is above 50%lift. By simply varying the inner surface of tapered insert 48 a usercan customize EGR valve 1 to match the desired valve characteristics tothe specific engine system architecture.

As can be seen by FIG. 7, the initial valve flow area and valve liftpercentages are essentially linear for all varieties of the taperedinsert design due to the initial radial gap between the valve head andthe flow varying surface of the insert. However, the valve flow areatapers off after the valve lift percentage exceeds that of about 17% forthe first tapered design (n=2.0) and up to about 33% of the last tapereddesign (n=0.5). These particular flow characteristics may be desired forgreater control of the flow areas at high lift conditions. The design ofEGR valve 1 provides greater controllability over a period of time thanthe existing EGR valve designs due to the ability to modify the flowcharacteristics of the valve structure using different inserts. Thepresent invention allows a user to select an insert design that meetsthe desired amount of flow control for a particular engine environment.

INDUSTRIAL APPLICABILITY

The flow control valve of the present invention may be employed in anyenvironment where it is essential to achieve a more desirablecharacteristic of exhaust gas recirculation flow control. Moreover, theflow control valve may be utilized where it is desirable to design theinput/output characteristics of the valve specifically for the needs ofa particular system. Furthermore, the flow control valve may be used tocontrol the degree to which Nox emission are reduced and othercharacteristics of interest, such as particulate emission and fueleconomy, are influenced.

What is claimed is:
 1. An exhaust gas recirculation (EGR) valve for aninternal combustion engine for controlling the flow of exhaust gas intoa cylinder combustion chamber comprising:a valve housing having acavity, an inlet passage and an outlet passage; a poppet valvepositioned in said cavity and including a reciprocally mounted valveelement and a valve seat, said valve element including a valve stem anda valve head integrally formed on said valve stem, said poppet valvebeing movable between an open position in which said valve element ispositioned a spaced distance from said valve seat to permit exhaust gasflow through said cavity and a closed position in which said valveelement engages said valve seat to block exhaust gas flow through saidcavity; a bias means for providing a positive force on said valve stemto create a seal between said valve head and said valve seat; and anexhaust gas flow varying means positioned in said cavity adjacent saidvalve element for controlling the exhaust gas flow rate from said inletpassage to said outlet passage during movement of said poppet valve,said exhaust gas flow varying means including an insert and a flowpassage formed in said insert, said insert including an inlet openingfor receiving exhaust gas from said inlet passage and directing theexhaust gas flow into said flow passage, and an outlet opening fordirecting the exhaust gas flow from said flow passage to said outletpassage; wherein movement of said valve element from said closed to saidopen position varies the effective cross-sectional flow area of saidflow passage, said insert including a tapered inner extent such thatsaid inlet opening has a different diameter than said outlet opening,and said insert is separably replaceable from said valve seat which isengaged by the valve element in said closed position.
 2. An exhaust gasrecirculation (EGR) valve for an internal combustion engine forcontrolling the flow of exhaust gas into a cylinder combustion chambercomprising:a valve housing having a cavity an inlet passage and anoutlet passage; a poppet valve positioned in said cavity and including areciprocally mounted valve element and a valve seat, said valve elementincluding a valve stem and a valve head integrally formed on said valvestem, said poppet valve being movable between an open position in whichsaid valve element is positioned a spaced distance from said valve seatto permit exhaust gas flow through said cavity and a closed position inwhich said valve element engages said valve seat to block exhaust gasflow through said cavity; a bias means for providing a positive force onsaid valve stem to create a seal between said valve head and said valveseat; and an exhaust gas flow varying means positioned in said cavityadjacent said valve element for controlling the exhaust gas flow ratefrom said inlet passage to said outlet passage during movement of saidpoppet valve, said exhaust gas flow varying means including an insertand a flow passage formed in said insert, said insert including an inletopening for receiving exhaust gas from said inlet passage and directingthe exhaust gas flow into said flow passage, and an outlet opening fordirecting the exhaust gas flow from said flow passage to said outletpassage; wherein movement of said valve element from said closed to saidopen position varies the effective cross-sectional flow area of saidflow passage said insert including a tapered inner extent such that saidinlet opening has a different diameter than said outlet opening, andsaid insert further includes a substantially straight portion inaddition to said tapered inner extent.
 3. An exhaust gas recirculation(EGR) valve of claim 2, wherein said substantially straight portiondefines said outlet opening, said outlet opening having a smallerdiameter than said inlet opening.
 4. An exhaust gas recirculation (EGR)valve of claim 2, wherein said substantially straight portion definessaid outlet opening, said outlet opening having a larger diameter thansaid inlet opening and said insert is separably replaceable from saidvalve seat which is engaged by the valve element in said closedposition.
 5. An exhaust gas recirculation (EGR) valve for an internalcombustion engine for controlling the flow of exhaust gas into acylinder combustion chamber comprising:a valve housing having a cavityformed therein; an inlet means formed in said valve housing fordirecting exhaust gas into said cavity; an outlet means formed in saidvalve housing for receiving exhaust gas from said cavity; a valve meansreciprocally mounted in said cavity for controlling fluid flow from saidinlet means to said outlet means, said valve means including a valvehead, a valve seat, and a cap, said valve head being movable between anopen position in which said valve head is positioned a spaced distancefrom said seat to permit exhaust gas flow through said cavity and aclosed position in which said valve head engages said valve seat toblock exhaust gas flow through said cavity; a sensing means attached tosaid cap for sensing the position of said valve means to provide anindication of the position of said valve head relative to said valveseat; and a flow varying means positioned adjacent said valve headdownstream of said valve seat for altering the flow rate of fluidbetween said inlet means and said outlet means, said flow varying meansincluding a first opening, a second opening positioned downstream ofsaid first opening and a flow varying surface extending between saidfirst and second openings and encircling said valve head when said valvehead is positioned between said first and said second openings to definea flow passage between said flow varying surface and said valve head,said flow varying surface having a predetermined shape such thatmovement of said valve head along said flow varying surface toward saidopen position varies an effective cross sectional flow area of said flowpassage so as to achieve a predetermined rate of increase in the flowrate of exhaust gas; wherein said movement of said valve head iscontinuously monitored by said sensing means and is controlled based onoperating conditions of said internal combustion engine, said flowvarying means including a removable insert, said flow varying surfacebeing formed on said insert and having a frusto-conically shaped portionand a substantially tubular portion.
 6. An exhaust gas recirculation(EGR) valve of claim 5, wherein said substantially tubular portiondefines said outlet opening, said outlet opening having a smallerdiameter than said inlet opening.
 7. An exhaust gas recirculation (EGR)valve of claim 5, wherein said insert is separably replaceable from saidvalve seat which is engaged by the valve element in said closedposition.
 8. An exhaust gas recirculation (EGR) valve of claim 1,wherein said outlet opening is larger than said inlet opening.
 9. Anexhaust gas recirculation (EGR) valve of claim 1, wherein said inletopening is larger than said outlet opening.
 10. An exhaust gasrecirculation (EGR) valve of claim 9, wherein said movement of saidvalve head is continuously monitored by a sensor and is controlled basedon operating conditions of said internal combustion engine.
 11. Anexhaust gas recirculation (EGR) valve of claim 9, further comprising asensor for sensing the position of said poppet valve to provide anindication of the position of said valve head relative to said valveseat.
 12. An exhaust gas recirculation (EGR) valve of claim 11, furthercomprising a cap positioned at one end of said poppet valve, saidbiasing means positioned in seated abutment against said cap.
 13. Anexhaust gas recirculation (EGR) valve of claim 12, wherein said sensoris attached to said cap.
 14. An exhaust gas recirculation (EGR) valve ofclaim 13, wherein said insert is substantially tubular in shape.
 15. Anexhaust gas recirculation (EGR) valve of claim 2, further comprising asensor for sensing the position of said poppet valve to provide anindication of the position of said valve head relative to said valveseat.
 16. An exhaust gas recirculation (EGR) valve of claim 15, whereinsaid insert is separably replaceable from said valve seat.
 17. Anexhaust gas recirculation (EGR) valve of claim 16, further comprising acap positioned at one end of said poppet valve, said biasing meanspositioned in seated abutment against said cap.
 18. An exhaust gasrecirculation (EGR) valve of claim 17, wherein said sensor is attachedto said cap.
 19. An exhaust gas recirculation (EGR) valve of claim 18,wherein said insert is substantially tubular in shape and saidsubstantially straight portion defines said outlet opening.
 20. Anexhaust gas recirculation (EGR) valve of claim 6, wherein said cap ispositioned at one end of said poppet valve and said biasing means ispositioned in seated abutment against said cap.